Project Leader(s): Anne-Marie Kitchen-Wheeler; Dr Edwards
Anne-Marie has been observing mantas in the Maldives in order to identify individuals and describe patterns of behaviour including migration patterns and social interactions.This is the first medium term study of the Maldives population of mantas and data collection began in 2001 and is on-going.
A manta identification method was devised and used in order to undertake mark-recapture data collection of the many mantas visiting reef areas known as cleaning stations located on opposite sides of the central Maldives atolls during the opposite monsoon weather patterns. The identifications were made from observation (photo, video and note records)in order to minimise disturbance of their natural behaviour. To present (May 2007), over 2300 encounters have been recorded and over 1400 different mantas have been identified and their physical characteristics recorded in a specially developed ACCESS database. The database includes the first official record of a "Black" manta in the Maldives. The identification method can be used to identify individuals from worldwide populations.
This data collection has resulted in the proving of the hypothesis that the mantas migrate from the east to the west side of the atolls with the movement of the plankton and the monsoon changes. In addition, other patterns in migrational have led to the development of other hypothesis in manta behaviour. These include an explanation of the large number of adult females regularly seen at the various cleaning stations (females 65.4% database compared to males 34.6%), the absence of large adult males seen at the majority of cleaning stations, and inter atoll migration of sub-adults and small adults of both sexes.
The database is currently being reviewed to ascertain the mating cycle of the Maldives manta population.
The mark recapture data has resulted in the Maldives having the highest known manta population in the world and allowed some atoll population estimates suggesting that the total manta population is in the tens of thousands.
Observation of the mantas has led to various novel behaviours being described including: courting where a male mounts female with the objective of having her accept him for mating, “practice” courting by juvenile males on pregnant females, mantas swimming through exhaled divers bubble streams and also swallowing the bubbles and expressing them through their gill slits, and extensive etiquette routines including threats, greetings, and complex group interactions.
Emeritus Professor Alasdair Edwards